We propose to investigate the following: 1) the role of proinsulin and of C peptide in the autoregulation of insulin secretion and to assess the relative significance of insulin synthesis and release in this phenomenon; 2) the ontogeny of gut glucagon in rats; 3) the regulation of glucagon secretion by incubated and perifused islets of obese and diabetic mice; 4) the possible role of glucagon insufficiency in clinical hypoglycemia; 5) the regulation of growth hormone secretion by the anterior pituitary of rats with growth hormone producing tumors.